1. Field of the Invention:
The present invention relates to a resistance temperature detector having quick response and high reliability for measuring the varying temperature of a high-pressure liquid such as a coolant in a pressurized water reactor and a mounting structure for the detector, and more particularly to a resistance temperature detector provided with both normal and backup temperature sensing elements.
2. Description of the Prior Art:
Operation and control of an atomic power plant are required to have extremely high safety, and hence, detectors for detecting various parameters to be used in that control, for instance, temperature detectors, are required to have high reliability. In a resistance temperature detector that is widely used, the most likely fault is a breakdown of a resistance wire, but since it is difficult to prevent this fault, it has been a common practice to provide normal and backup resistance temperature detectors.
FIG. 12 shows a cross-section of one example of a prior art resistance temperature detector for measuring the temperature of a high-pressure fluid.
In a resistance temperature detector 1, a ceramic sinter-type temperature sensing resistance element 3 is disposed within a protective case 2, and the space within the protective case 2 is filled with filler material 4 consisting of magnesium oxide (MgO). As shown in FIG. 13, within the ceramic sinter type temperature sensing resistance element 3 is assembled a double element 5, and lead wires 6 of the double element 5 are connected to an integral sheath cable (not shown).
The resistance temperature detector 1 is disposed within the fluid, and temperature measurement for the fluid is carried out.
In addition, FIG. 14 shows a cross-sectional side view of a prior art well for a resistance temperature detector.
A well structure for a resistance temperature detector (hereinafter abbreviated as "RTD well structure") 101 is mounted by welding tube stub 103 to a pipe 102 through which highly pressurized fluid flows. RTD well structure 101 is formed with a single insert portion 104 in which a resistance temperature detector (hereinafter abbreviated as "RTD") is inserted and held, and the tip end of the insert portion 104 is positioned within the pipe 102.
The fluid flowing through the pipe 102 comes into contact with the tip end of the insert portion 104, and the temperature of the fluid within the pipe 102 is measured by the RTD inserted and held in the insert portion 104.
With regard to this type of resistance temperature detector, in order to insure continuity of control it is desirable to dispose dual temperature detectors, that is, normal and backup temperature detectors at the same location.
Moreover, since the temperature of a coolant could vary abruptly, the RTD must have a quick response rate.
Futhermore, the response rate may possibly be degraded during use of the temperature temperatures detector.
Therefore, in order to insure safety and reliability of control, it has been increasingly demanded to dispose a plurality of temperature detectors at the same location, to continuously check soundness of the temperature detectors during a controlled operation, and to use the output of the temperature detector operating normally.
Accordingly, a resistance temperature detector which meets the above-mentioned demands is desirable.
However, the above-described prior art temperature detector 1 shown in FIG. 12 involved multiple problems. First, as an unseparated double element 5 was used, if any fault occurred in the resistance temperature detector 1, it was impossible to continue measurement at the same location by means of a backup resistance temperature detector. Second in the resistance temperature detector 1 of the prior art, since the filler material 4 filled the protective case 2 and the ceramic sinter type temperature sensing resistance element 3 was buried within the filler material, the inside of the protective case 2 was not hollow, the thermal inertia of that portion of the protective case 2 was increased by the existence of the filler material 4, and also, since the ceramic sinter type temperature sensing resistance element 3 was not held in tight contact with the inner wall surface of the protective case 2, delay of heat transmission from the outside occurred. Accordingly, these factors restricted the response rate of the resistance temperature detector 1. In addition, since the filler material 4 consisted of magnesium oxide, its hygroscopicity was high. Third, as the sheath cable was of an integral type, where two resistance temperature detectors 1 consisting of, for instance, normal and backup temperature detectors were used, degradation of insulation due to high temperature could occur between the lead wires 6, causing a shunt circuit to be created between the lead wires 6. Therefore, in an important temperature measuring system there was a possibility that a serious problem might result.
Furthermore, in the above-described prior art RTD well structure 101 shown in FIG. 14, as only one insert portion 104 was formed, the number of RTD's that could be held in one RTD well structure 101 was limited to one. Accordingly, in the event that in a temperature measuring scheme making use of RTDs it is required to provide a backup RTD in addition to a normal RTD, an additional RTD well structure 101 must be provided at a separate location. In order to to provide an additional RTD well structure 101, it is necessary to provide a new hole and a new tube stub 103 on the pipe 102, and hence material and labor costs are increased. In addition, while the normal RTD and the backup RTD should measure the temperature at the same location, in the case where the additional RTD well structure 101 is provided at a separate location, the normal and backup RTDs necessarily perform temperature measurement at separate fluid locations, that is, at locations where thermo-hydraulic conditions are different, resulting in the applicability of the measurement by the backup RTD being reduced.